At 15 people were injured by the blast on Monday morning. A one-year-old baby is reported to be among the victims.

The explosion was set off by a suicide bomber, spokesman for the Russian Investigative Committee, Vladimir Markin, confirmed.

The bomb may have been planted in the central part of the trolley bus rather than brought in by a suicide bomber, said the National Antiterrorist Committee.

The bus was near one of the city markets when the explosion happened. The site has been cordoned off, with traffic diverted to other streets.

The blast wave was powerful enough to shatter some windows in nearby buildings.

The Emergencies Ministry said it is preparing a new flight from Moscow to Volgograd with medical equipment and personnel for possible transportation of the blast victims to the capital.

The new deaths in Volgograd come just a day after a suicide bomber targeted the city’s railway station, killing 14 people on the spot and injuring more than 30 others. Three of those injured succumbed to their wounds in hospital.

And in October the city witnessed yet another terrorist attack, when a suicide attacker set off an explosion in a bus heading to Moscow, killing 6 people and injuring almost 40.